Assessing

Introduction

Assessment is the process of gathering and evaluating information in a way that facilitates decision making. Through methods such as ranking systems, geospatial analysis, inventory/survey, and monitoring, assessments can provide a more accurate picture of problems and solutions associated with plant invasions so that land managers are better equipped to identify feasible management strategies, develop measurable objectives, select safe and effective methods, and evaluate program outcomes. Ranging from simple to complex, assessment activities should be designed to accommodate a project's specific needs and resources available for management.

In this module, you will become familiar with

the purpose and need for assessment in invasive plant management

a framework for assessing risk associated with plant invasions

applying invasive plant assessments to management

fundamentals of invasive plant inventory/survey

approaches to invasive plant monitoring

Role of Assessment in Invasive Plant Management

What is Assessment?

Assessment can refer to a number of activities used to achieve different goals. In the context of managing invasive plants, assessment is the process of gathering and evaluating information about the nature, quality, ability, extent, or significance of the many factors that influence invasive plant management decisions. These factors may include distribution, abundance, and impacts of invasive plants; ecological characteristics and conditions of a management area; and costs and effects of management activities, all within the context of operational constraints and socioeconomic factors. Assessment is ongoing and integrated throughout the invasive plant management process, evaluating new information and knowledge as it is acquired.

Why Conduct Assessments?

Assessment is an important element of invasive plant management, providing a basis and rationale for management decisions that address newly invading, as well as established invasive plant populations. Assessments support developing and maintaining plans and/or programs for invasive plant management that are consistent with the standards of knowledge-intensive management frameworks, such as Integrated Pest Management (IPM) or Adaptive Management.

Knowledge gained from assessments can provide a deeper understanding of the problems and solutions associated with plant invasions so that land managers are better equipped to

identify management strategies and options

establish measurable management objectives and action thresholds

select safe and effective management methods

evaluate program outcomes

Risk and Invasive Plant Management

Risk is defined as the product of the likelihood and consequences of an event or process, such as
a plant invasion or perhaps the management actions taken to control an invasive plant population
(National Research Council 2002). Managing invasive plant populations within an IPM framework is
essentially a form of risk management, where invasive plants or the methods used to control them
may present a threat (risk) to land management goals for a valued resource such as an ecological
community.

Risks associated with plant invasions and their management are highly variable and not fully understood.

Invasive plant species differ in the likelihood and consequences of their establishment and spread, and in their susceptibility to management actions.

Ecological communities differ in the values society, policy, and directives attach to them, in their vulnerability to invasion, and in their susceptibility to unintended effects of management actions.

Plant species or populations that are the intended object of a management activity or action are referred to as targets, and those plants or resources that are not the intended object are referred to as nontargets. Land managers are often tasked with managing large tracts of land where complete prevention or control of all target invasive plant populations would be economically or ecologically impossible. In addition to other demands required to adequately manage National Wildlife Refuge (NWR) System lands, operational resources must be allocated among current and potential invasions through a process of balancing risks, costs, and benefits. Managing invasive plants in terms of minimizing risk-whether it is economic, environmental, or societal risk-requires a thorough understanding of the problem (invasive plants) and the alternative solutions (management actions).

Framework for Assessment

The National Research Council (2002) suggests that a risk assessment framework has the most
practical value for prioritizing management actions because risk assessments are designed to
evaluate both the likelihood and consequences of events such as the establishment and spread of
invasive plants and/or the effects of methods used to control them.

The US Department of Agriculture and other government agencies have been using a risk
assessment framework to address invasive species for several years, primarily to evaluate the
potential invasiveness of proposed imported plant species and to identify susceptible resources
(e.g., agricultural commodities, ecological communities, or property) and pathways of established
species (APHIS 2004, EPA 1998). The ecological risk assessment framework published by the
Environmental Protection Agency (1998) has been adapted to evaluate risk for invasive species
(see Suedel et al. 2007) and invaded habitats (see Stohlgren and Schnase 2006).

The goals of large-scale assessment frameworks that address risks associated with plant invasions
on a national level are essentially the same as those that are applied to small-scale assessments for
local management areas:

evaluate the risk of introduction and establishment of potential invasive plant populations

allocate resources to control existing invasive plant populations

Regardless of scale and scope, assessments that follow a risk assessment framework consist of
three major phases.

Risk Assessment Framework Phases

1. Problem
formulation

a planning and scoping process that establishes the goals, breadth, and focus of the assessment

a process of information gathering and evaluation used to develop “exposure and effect” profiles of the invasive plants within the context of affected ecological communities

exposure = likelihood of introduction, establishment, and spread; effect = probability and severity of economic and ecological consequences of invasion

3. Risk
characterization

compares exposure and effect profiles using a variety of techniques to draw conclusions and make decisions

Within this basic framework, assessments can be conducted in a variety of ways to achieve different outcomes. They can be simple, rapid, and inexpensive; or complex, time-intensive, and costly. While assessments should be conducted in a way that provides sufficient information and understanding to make sound decisions that support management goals, it is important to conduct the best assessment possible within a reasonable time frame and budget.

Prior to initiating an assessment, it will be important to consider the overall goals and objectives
of the assessment, the scale and scope, the type and detail of data to be used, and methods for
collecting and analyzing data and making decisions.

Considerations for Conducting Assessments

Goals and objectives

An important first step for conducting an assessment is establishing the purpose and desired outcomes, and how the outcomes will contribute to management objectives and overall land management goals.

Scale and scope

Resources are rarely available to thoroughly assess risks associated with all invasive plant species at all sites within a managed area. For detailed assessments, it is often necessary to narrow the scope and scale of an assessment to include only a few target species, or a small area or ecological site. More general assessments may include a number of species across larger areas.

Data type and
detail

An important step for preparing to conduct an assessment is deciding what type of information (e.g., qualitative or quantitative) is needed to meet the requirements of established goals and objectives. It is important to consider how the data will be used, the level of detail required, what information is already available, and whether the required standards for data are feasible considering the operational resources required to collect them.

Analysis and
decision making

Decision making processes are used to analyze and evaluate assessment information. In general, management decisions are made in one of three ways: judgment and expertise of land managers, precedent of what has been done before, or through a formal analysis. The judgment of experienced professionals is irreplaceable in decision making. However, a formal analysis provides a consistent, objective approach for making
decisions, as well as well-documented justification for those decisions.

Several assessment systems have been devised for characterizing plant species in terms of
their invasiveness, impacts, and feasibility of control; and for characterizing areas in terms of
their ecological value or vulnerability to invasion. Together, these systems can help identify which
invasive plant species are likely to invade and be disruptive in a particular area, and which areas
are most susceptible to invasion by which species. This knowledge can be applied to prioritizing
prevention and control efforts to specific areas and invasive plant populations.

Characterizing Species

Although an inventory or survey of an area may indicate there are a number of undesirable
plant species present, only a small percentage may become invasive and cause harm. Those
species that are considered to be invasive will vary in likelihood and consequences (risk) of their
establishment in ecological communities, and differ in their susceptibility to management methods. It
may be prudent to prioritize work efforts towards those species or populations that are most likely to
establish and spread, most likely to cause harm, and most likely to be successfully controlled.

One way to prioritize management actions is use a ranking system that helps separate innocuous
species from disruptive species. This separation allows land managers to then concentrate efforts
on species in the disruptive category. Ranking systems are also designed to identify those species
that have the potential to become a threat.

After a user inputs data about species characteristics, site characteristics, and control difficulty, the Alien Plants Ranking System computer program produces a report that ranks species by plotting relative impacts against feasibility of control.

Several systems have been designed to assist in ranking or
prioritizing species at various spatial scales (see Hiebert and
Stubbendieck 1993, APRS Implementation Team 2001, Morse
et al. 2004, Cal-IPC 2006, Pheloung et al. 1999). Species
ranking systems typically use a numeric scoring system to
assess species based on their abundance and distribution,
innate ability to be invasive, current or potential impacts,
and management difficulty. Although most systems account
for some level of uncertainty, the user should be able to
accurately answer questions about the ecology, biology, and
control methods for each species.

The Alien Plants Ranking System (APRS) is a computer
application that analyzes user-provided data about a species'
impacts, invasiveness, and ease of control within the context
of a specific ecological site. Based on successful application
to National Park System lands and other areas such as Silvio
O. Conte NWR, the US Fish and Wildlife Service (USFWS) is
exploring ways that APRS can be adapted as a standardized
ranking and prioritizing system for refuges.

Applying a standardized systematic method for assessing and
prioritizing invasive plant species on a small scale can provide
valuable site-specific information relevant for management in
a particular area. When applied as part of a coordinated effort,
a standardized ranking system can contribute to developing
priorities on a regional or national scale.

An Informal Ranking System: Invasive Free Zone Management Plan

The Whittlesey Creek NWR in Wisconsin, along with numerous agencies and individuals, prioritized invasive species using an informal ranking system.

Resource professionals involved in the project ranked invasive plant species for the "Invasive Free Zone" management plan based on their experience and knowledge of species invasiveness.

As more data are available from inventory/survey and monitoring, invasiveness rankings will be reassessed and adjusted as needed.

Characterizing Sites

Ecological communities differ in their susceptibility to invasion. Characterizing sites that have
been invaded or are susceptible to invasion can provide valuable insight for prioritizing areas for
prevention or early detection strategies, or for prioritizing populations for control based on their
location in high priority areas (e.g., areas with high ecological value or high susceptibility).

Researchers have attempted to identify general site attributes and conditions that make some
ecological communities more susceptible to invasion than others (see Stohlgren et al. 2002,
Endress et al. 2006). Others have described ecological communities in terms of their susceptibility
to invasion by one or more particular invasive plant species (see Mantas 2003, Shafii et al. 2003,
Rice 2007, Rew et al. 2005, Martin et al. 2007). Both approaches consider site characteristics and
conditions that may promote establishment and spread of invasive plants. The latter approach
also requires knowledge about the invasive plant species such as habitat requirements, life history
characteristics, and other factors that may influence a plant's establishment and survival.

Geospatial database analysis is often used to characterize and prioritize sites in terms of
vulnerability to invasion. Geographic Information System (GIS) computer software can be used to
analyze complex combinations of spatial data and develop models and maps that identify areas
where plant invasions have a high probability of occurrence and where they may have the greatest
impacts. Extensive GIS databases are available for most federally managed lands and include
attributes such as elevation, geological character, soil associations, vegetation types, habitats,
land use, etc. Invasive plant inventory/survey and monitoring data can be incorporated into a GIS
database and analyzed with other ecological data to identify susceptibility or resistance of ecological
communities to plant invasions.

NASA/USGS Invasive Species Forecasting System

The Invasive Species Forecasting System is an information management and modeling environment.

The NASA Office of Earth Science and the US Geological Survey
are working together to develop a National Invasive Species
Forecasting System for the early detection and management of
invasive species on Department of Interior and adjacent lands.

The forecasting system provides a framework for using predictive
geospatial models to process NASA and commercial data to
create on-demand, local- and regional-scale maps of invasive
species patterns and vulnerable habitats.

When fully implemented, the web-based forecasting system will
provide a dynamic and flexible mechanism for generating maps of
areas with high potential for nonnative species invasions.

Assessing Management Alternatives

Managing large acreages with limited means requires careful allocation of resources to areas
with the highest return. The economic and ecological costs and benefits of various management
activities are often used to prioritize invasive plant management actions and guide efforts towards
those areas that are considered to be the most valuable and/or have a high probability of success.

Management methods applied to control invasive plants can have environmental and economic
consequences. For example, the use of chemicals to manage invasive plants has risks, many of which are
assessed during the Environmental Protection Agency's process for registering an herbicide.
Similarly, classical biological control agents undergo rigorous testing that evaluates their potential
impacts and risks prior to their release in the United States. Other methods such as prescribed
grazing, prescribed burning, or physical methods are not federally regulated, but may present some
risks as well.

potential nontarget or side effects a method may have in a particular ecological setting

The potential impacts associated with various management alternatives proposed for federal
lands, such as NWR System lands, are typically evaluated in Environmental Assessments or
Environmental Impact Statements required by the National Environmental Policy Act. On refuges,
impacts of proposed management activities are further evaluated during development of Habitat
Management Plans or Comprehensive Conservation Plans, and sometimes examined in more detail
in Integrated Pest Management Plans or Invasive Species Management Plans.

Applying Assessments to Management

Knowledge gained from assessments-risk assessments, inventory/survey, and monitoring-
provides a basis for making management decisions fundamental to the invasive plant management
process. Through a deeper understanding of relative risks associated with invasive plants and
accurate assessment of population status and trends, land managers can determine when control
action is necessary, establish measurable achievable objectives, and select feasible management
strategies and options.

Action Thresholds and Management Objectives

Action thresholds are helpful in prioritizing and selecting management strategies and options.
An action threshold is the invasive plant population level at which a decision is made that some
intervention is needed. Originally developed for agricultural systems where economic damage
is measurable, action thresholds are more difficult to determine for invasive plants occurring in
wildland ecosystems (see Briske et al 2006, Brown et al. 1999, Coble and Mortensen 1991).

By conducting invasive plant assessments, levels of acceptable and unacceptable risk or damage
are more clearly defined. For example, action thresholds may reflect a very low tolerance for high
risk invasive plants in high value areas, whereas an abundance of low risk species occurring in low
value areas may be tolerated before action is required.

Management objectives that describe desired invasive plant population levels in specific and
measurable terms may help define action thresholds in some situations. For example, in an
area where low densities of an invasive plant occur, management objectives may be to maintain
population levels at or below the current density. Until densities exceed that level no management
action is required, but the site may be monitored instead. When monitoring detects densities at
or above acceptable levels, the site may be made a higher priority for management action. When
invasive plant populations are successfully reduced to the desired (acceptable) level within a plant
community, management actions may be stopped.

For small, localized populations, delaying actions can result in increased cost of control and
decreased chance of success (Hobbs and Humphries 1995). Therefore, management objectives for
newly invading populations often reflect very low action thresholds.

Management Strategies and Options

Invasive plant assessment activities that describe current status and trends in distribution and
abundance of invasive plant populations (i.e., inventory/survey and monitoring) can help identify
appropriate management strategies by characterizing the phase of the plant invasion process for
populations.

Preventing invasive plants from becoming established is less expensive, less time-consuming,
and more effective than trying to control them after they have become widespread or have had
significant ecological impacts. Prevention can be applied only to invasive plant species that do not
occur on the site or in areas where invasive plant species do not occur. It requires identification of
potential invaders, awareness of vectors and pathways of introduction, mechanisms of reproduction
and spread, habitat requirements, and conditions that favor the species. Assessments can help
identify areas where invasive plant populations do not occur as well as habitats that may be
particularly susceptible to introduction and spread of new infestations.

Early Detection

Once unwanted plants begin to invade an area, detecting and controlling invasions when they are
small and localized provides the next best return. Early detection and rapid response (EDRR) is the
key to eliminating the plants before their population expands.

Detecting and responding to plant invasions requires a complex series of actions that can be
grouped into three main categories:

EDRR efforts are designed to DETECT new invasive plants in time to allow efficient and
environmentally sound ASSESSMENTS to be made; and RESPOND to invasions in an effective,
environmentally sound manner that will prevent the spread and permanent establishment of
invasive species. Ranking systems and GIS analysis can help prioritize plant species or areas that
will be targeted for EDRR strategies. Inventory/surveys and monitoring activities can be designed
specifically to detect new invasive plant populations when they are small.

Control

As populations begin to expand, control strategies may be required, demanding significantly more
resources. Control options will depend on the compatibility of available management methods and
technology with the characteristics of the infestation (size, abundance, and distribution), invasive
plant characteristics, ecological and environmental conditions, and available resources (budgets,
personnel, training, etc.). Control options can be grouped as follows:

Control Options

Eradication

eliminate all invasive plants and their propagules

practical on small-scale infestations, generally in the introduction phase

prevent large infestations of invasive plants from spreading to uninfested areas

may involve methods that prevent reproduction and propagule dispersal, treating the perimeter of a large infestation, or eliminating small satellite infestations

Multiple strategies and options are often applied to manage a complex of invasive plant infestations throughout a management area.

A Typical Prioritization Scheme for Management Strategies and Control Options

1
Strategy: Prevention

prevent new infestations from becoming established

2
Strategy: Control

eradicate small or isolated “satellite” infestations

3
Strategy: Control

contain the perimeter of large “core” infestations

4
Strategy: Control

suppress the interior of large “core” infestations

Restoration

Extensive, naturalized infestations may be beyond feasible control with conventional methods
because the desirable plant community composition may not be sufficient to fill niches left open
by controlled/suppressed invasive plants, invasive plant populations have altered the site, or other
reasons. In these cases, further efforts may be necessary to restore the site. Restoration can
be very labor intensive and costly. Restoration may be considered for high value areas that are
relatively small. Assessment can help determine if expending resources into extensive restoration is
worth the relative benefit.